The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Vast numbers of automatic transmissions installed in motor vehicles utilize a plurality of friction clutches and brakes. Basically these devices include a first plurality of clutch plates or discs coupled to a first member which are interleaved with a second plurality of clutch plates or discs coupled to a second member. An adjacent actuator which may be electrically, hydraulically or pneumatically powered engages and releases the device. If the device is a clutch both members are capable of rotation and one is typically an input and the other an output. If the device is a brake, one member is capable of rotation and the other is grounded (stationary).
As common as these devices are, and because of this, given the engineering effort expended upon them, it may be surprising that they are not without their drawbacks. When these devices are utilized in automatic transmissions, typically between components of planetary gear assemblies, the speed across an open clutch or brake may exceed 5,000 r.p.m. Operation at such speeds invariably results in heat generation which in itself can be an issue but which also results in spin losses and reduces the efficiency of the transmission and the entire powertrain. Reducing the speed across the clutch or brake is one possible solution but it often involves many operational compromises. Accordingly, research directed to the problem of reducing clutch drag at all operating speeds is ongoing and the present invention is the result of such research.